The use of conductivity measurements to analyze various characteristics of human tissue specimens has been shown to yield many practical advantages. For example, conductivity measurements may be used to distinguish diseased tissue from healthy tissue. Both conventional electrode and induction coil methods have been used to perform conductivity measurements of human tissue specimens.
Conventional electrodes for measuring conductivity of a human tissue typically apply an AC voltage to a specimen of interest. The current traveling through the specimen is measured and the conductivity is computed. In some cases, many electrodes are attached so that imaging of the specimen is made possible in circumstances where conductivity varies spatially through the specimen.
A disadvantage of conventional electrodes is that it requires direct electrical contact with the tissue specimen. This is particularly true for human tissue specimens because the stratum corneum layer of the epidermis impedes the flow of current through the specimen, leading to variable conductivity measurements. Conventional electrodes may also exhibit electrode polarization, resulting in inaccurate conductivity measurements.
Induction coil methods and devices for measuring conductivity have used a wide variety of induction coil designs including solenoids or simple loop type coils consisting of a few turns of wire. These coils may probe the human tissue specimen at depths allowing interferences from bone and/or internal organs that distort the conductivity measurement. Many of these devices also involve the use of expensive instrumentation to measure coil related parameters such as complex impedance and use circuitry that permits the induction coil to deviate from resonance as the coil is placed adjacent to a specimen, making measurement of conductivity more difficult.
D. Haemmerich, S. T. Staelin, J. Z. Tsai, “In vivo electrical conductivity of hepatic tumors,” Physiological Measurement Vol. 24, pp. 251-260 (2003) discusses the use of conventional electrode methods to measure electrical conductivity of hepatic tumors to demonstrate that abnormal, or diseased, tissues exhibit different electrical properties than healthy tissues.
L. W. Hart, H. W. Ko, J. H. Meyer, D. P. Vasholz, and R. I. Joseph, “A noninvasive electromagnetic conductivity sensor for biomedical applications,” IEEE Transactions on Biomedical Engineering, Vol. 35, No. 12, pp. 1011-1022 (1988) discusses the use of conductivity measurements to identify the presence of edema in brain tissues.
While various methods and apparatus for assessing health of human tissue using conductivity measurements have been developed, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology.